Vaatu was the Bigger Bad of the series from what I can tell while his henchman had his own agenda to achieve and does everything. The Emperor Palpatine in the original trilogy was considered the Bigger Bad while Darth Vader was the Big Bad due to him having more to do with the plot. A character of the series can't be both. Palpatine was the Big Bad of the prequels due to being far more active and center of the plot all the while his enforcers being just figure heads who just do as their told.
He seems more of Palpatine from the original trilogy. He's important but not the main threat the heroes are forced to confront for a majority of the season. All the info I've read leads me to see him only as the Bigger Bad. I rather just state my point here then edit war and rather you do the same.